Call Signaling
In many packet switching applications, a user may require some minimal quality of service (QoS) from the network so that it can work properly. In general, an application will request the network to provide the required QoS by encoding the QoS parameters in the call signaling messages.
For example, consider Long Term Evolution (LTE) from 3rd Generation Partnership Project (GPP), which is the next generation technology and architecture for 3GPP.
In LTE, user equipment (UE) will send and receive user packets through its designated PDN-GW (Public data network-gateway). The PDN-GW will forward the data packet from the UE to its intended destination. It also accepts packets on the behalf of the UE, and then forwards the arriving packets to the UE. (Note that there are other network elements such as the eNodeB and the S-GW between an UE and the PDN-GW)
The logical connection between the UE and the PDN-GW is referred to as the EPS (Evolved Packet System) “bearer” (or bearer for short). Associated with each bearer is a QoS (Quality of Service) profile which governs how packets of this bearer should be treated by the network. As a UE may have multiple concurrent sessions, each with a different QoS needs, multiple bearers can be set up between an UE and the PDN-GW, each supporting a different QoS. Multiple sessions of the same QoS class can be mapped onto the same bearer.
When a UE wants to set up an EPS bearer to the PDN-GW, it will send a Bearer Resource Modification request message to the PDN-GW. The message includes the following information (with other information):                Service data flow templates which are used by the gateways to detect packets that belongs to a data flow, upstream and downstream.        QCI-QoS class identifier which defines the level of service required (such as the packet loss rate and delay)        Upstream (UL) and downstream (DL) maximum bit rate (MBR)        Upstream and downstream guaranteed bit rate (GBR)        Allocation and Retention Priority (ARP) parameter, which specifies the priority of the call for call admission and, when in congestion, whether it can preempt a lower priority call or be preempted by higher priority call.The QCI, MBR, GBR, ARP are collectively referred to as the QoS parameters of the bearer.        
There are other call signal protocols that provides QoS request. A well known example is the Session Initiation Protocol (SIP) from the Internet Engineering Task Force (IETF).
Call Admission and Call Preemption
When a user requests a specific QoS level for a call from the network, the network may not have enough resources to support the call and maintain the QoS level as requested. In these instances, the network would not admit the call and the call is blocked. However, the incoming call may be of high priority and network operator may want to admit the incoming high priority call at the expense of the lower priority established calls. In these instances, preemption would take place. Lower priority call(s) would be disconnected to free up enough resources so the higher priority call would be admitted. The selection of which calls to be preempted depends on the policy of network operator, as well as the capabilities of the equipment.
Multiple Bit-Rate Applications
Many applications can operate at multiple bit-rate levels. Consider streaming video as an example. The nominal speed for a particular video encoder may be 10 Mbps. An application may be willing to transmit at ¼ the nominal speed by reducing the screen size (½ the height and ½ the width). Therefore, the speed now is 2.5 Mps. By accepting B&W and forgoing color, a reduction of another 50% could be achieved. Reducing the frame rate of a streaming video application can be another method of reducing the bandwidth required, as would using a different compression algorithm or controlling parameters of a compression algorithm.
In view of the foregoing it would be desirable to provide an improved system and method for call admission and preemption to take advantage of flexibility of multiple bit-rate applications.